Eliminate Sawing-Induced Peeling Through Forming Trenches

ABSTRACT

A package includes a device die, a molding material encircling the device die, wherein a top surface of the molding material is substantially level with a top surface of the device die, and a bottom dielectric layer over the device die and the molding material. A plurality of redistribution lines (RDLs) extends into the bottom dielectric layer and electrically coupling to the device die. A top polymer layer is over the bottom dielectric layer, with a trench ring penetrating through the top polymer layer. The trench ring is adjacent to edges of the package. The package further includes Under-Bump Metallurgies (UBMs) extending into the top polymer layer.

CROSS REFERENCE

This application is a continuation of U.S. application Ser. No.15/443,678, entitled “Eliminate Sawing-Induced Peeling Through FormingTrenches,” filed Feb. 27, 2017, which is a continuation of U.S.application Ser. No. 14/713,935, entitled “Eliminate Sawing-InducedPeeling Through Forming Trenches,” filed May 15, 2015, now Pat. No.9,589,903 issued Mar. 7, 2017, which claims the benefit of U.S.Provisional Application No. 62/133,770, entitled “EliminateSawing-Induced Peeling Through Forming Trenches,” filed on Mar. 16,2015, which application is hereby incorporated herein by reference.

BACKGROUND

With the evolving of semiconductor technologies, semiconductorchips/dies are becoming increasingly smaller. In the meantime, morefunctions need to be integrated into the semiconductor dies.Accordingly, the semiconductor dies need to have increasingly greaternumbers of I/O pads packed into smaller areas, and the density of theI/O pads rises quickly over time. As a result, the packaging of thesemiconductor dies becomes more difficult, which adversely affects theyield of the packaging.

Conventional package technologies can be divided into two categories. Inthe first category, dies on a wafer are packaged before they are sawed.This packaging technology has some advantageous features, such as agreater throughput and a lower cost. Further, less underfill or moldingcompound is needed. However, this packaging technology also suffers fromdrawbacks. Since the sizes of the dies are becoming increasinglysmaller, and the respective packages can only be fan-in type packages,in which the I/O pads of each die are limited to a region directly overthe surface of the respective die. With the limited areas of the dies,the number of the I/O pads is limited due to the limitation of the pitchof the I/O pads. If the pitch of the pads is to be decreased, solderbridges may occur. Additionally, under the fixed ball-size requirement,solder balls must have a certain size, which in turn limits the numberof solder balls that can be packed on the surface of a die.

In the other category of packaging, dies are sawed from wafers beforethey are packaged. An advantageous feature of this packaging technologyis the possibility of forming fan-out packages, which means the I/O padson a die can be redistributed to a greater area than the die, and hencethe number of I/O pads packed on the surfaces of the dies can beincreased. Another advantageous feature of this packaging technology isthat “known-good-dies” are packaged, and defective dies are discarded,and hence cost and effort are not wasted on the defective dies.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1 through 16 are cross-sectional views and top views ofintermediate stages in the manufacturing of packages in accordance withsome embodiments;

FIGS. 17 through 20 are cross-sectional views of packages in accordancewith alternative embodiments;

FIG. 21 illustrates a top-view of packages in accordance with someembodiments;

FIG. 22 illustrates a top-view of a sawed package in accordance withsome embodiments; and

FIG. 23 illustrates a process flow in the formation of a package inaccordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “underlying,” “below,”“lower,” “overlying,” “upper” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

A package and the method of forming the same are provided in accordancewith various exemplary embodiments. The intermediate stages of formingthe package are illustrated. The variations of the embodiments arediscussed. Throughout the various views and illustrative embodiments,like reference numbers are used to designate like elements.

FIGS. 1 through 16 illustrate the cross-sectional views of intermediatestages in the formation a package in accordance with some embodiments.The steps shown in FIG. 1 through 16 are also illustrated schematicallyin the process flow 300 shown in FIG. 23. In the subsequent discussion,the process steps shown in FIGS. 1 through 16 are discussed referring tothe process steps in FIG. 23.

FIG. 1 illustrates carrier 20 and release layer 22 formed on carrier 20.Carrier 20 may be a glass carrier, a ceramic carrier, or the like.Carrier 20 may have a round top-view shape and may have a size of asilicon wafer. For example, carrier 20 may have an 8-inch diameter, a12-inch diameter, or the like. Release layer 22 may be formed of apolymer-based material (such as a Light To Heat Conversion (LTHC)material), which may be removed along with carrier 20 from the overlyingstructures that will be formed in subsequent steps. In some embodiments,release layer 22 is formed of an epoxy-based thermal-release material.In other embodiments, release layer 22 is formed of an ultra-violet (UV)glue. Release layer 22 may be dispensed as a liquid and cured. Inalternative embodiments, release layer 22 is a laminate film and islaminated onto carrier 20. The top surface of release layer 22 isleveled and has a high degree of co-planarity.

Dielectric layer 24 is formed on release layer 22. In accordance withsome embodiments of the present disclosure, dielectric layer 24 isformed of a polymer, which may also be a photo-sensitive material suchas polybenzoxazole (PBO), polyimid, or the like, that may be easilypatterned using a photo lithography process. In alternative embodiments,dielectric layer 24 is formed of a nitride such as silicon nitride, anoxide such as silicon oxide, PhosphoSilicate Glass (PSG), BoroSilicateGlass (BSG), Boron-doped PhosphoSilicate Glass (BPSG), or the like.

Referring to FIG. 2, Redistribution Lines (RDLs) 26 are formed overdielectric layer 24. The respective step is shown as step 310 in theprocess flow shown in FIG. 23. RDLs 26 are also referred to as backsideRDLs since they are located on the backside of device die 36 (FIG. 5).The formation of RDLs 26 may include forming a seed layer (not shown)over dielectric layer 24, forming a patterned mask (not shown) such as aphoto resist over the seed layer, and then performing a metal plating onthe exposed seed layer. The patterned mask and the portions of the seedlayer covered by the patterned mask are then removed, leaving RDLs 26 asin FIG. 2. In accordance with some embodiments, the seed layer comprisesa titanium layer and a copper layer over the titanium layer. The seedlayer may be formed using, for example, Physical Vapor Deposition (PVD).The plating may be performed using, for example, electro-less plating.

Referring to FIG. 3, dielectric layer 28 is formed on RDLs 26. Thebottom surface of dielectric layer 28 is in contact with the topsurfaces of RDLs 26 and dielectric layer 24. In accordance with someembodiments of the present disclosure, dielectric layer 28 is formed ofa polymer, which may be a photo-sensitive polymer such as PBO,polyimide, or the like. In alternative embodiments, dielectric layer 28is formed of a nitride such as silicon nitride, an oxide such as siliconoxide, PSG, BSG, BPSG, or the like. Dielectric layer 28 is thenpatterned to form openings 30 therein. Hence, RDLs 26 are exposedthrough the openings 30 in dielectric layer 28.

Referring to FIG. 4, metal posts 32 are formed. Throughout thedescription, metal posts 32 are alternatively referred to asthrough-vias 32 since metal posts 32 penetrate through the subsequentlyformed molding material. The respective step is shown as step 312 in theprocess flow shown in FIG. 23. In accordance with some embodiments ofthe present disclosure, through-vias 32 are formed by plating. Theplating of through-vias 32 may include forming a blanket seed layer (notshown) over layer 28 and extending into openings 30 (FIG. 3), formingand patterning a photo resist (not shown), and plating through-vias 32on the portions of the seed layer that are exposed through the openingsin the photo resist. The photo resist and the portions of the seed layerthat were covered by the photo resist are then removed. The material ofthrough-vias 32 may include copper, aluminum, or the like. Through-vias32 have the shape of rods. The top-view shapes of through-vias 32 may becircles, rectangles, squares, hexagons, or the like.

FIG. 5 illustrates the placement of device dies 36. The respective stepis shown as step 314 in the process flow shown in FIG. 23. Device dies36 are adhered to dielectric layer 28 through Die-Attach Films (DAFs)45, which may be adhesive films. Device dies 36 may be logic device diesincluding logic transistors therein. In some exemplary embodiments,device dies 36 are designed for mobile applications and may be PowerManagement Integrated Circuit (PMIC) dies, Transceiver (TRX) dies, orthe like.

In some exemplary embodiments, metal pillars 38 (such as a copper post)are pre-formed as the topmost portions of device dies 36, wherein metalpillars 38 are electrically coupled to the integrated circuit devicessuch as transistors in device dies 36. In accordance with someembodiments of the present disclosure, a polymer fills the gaps betweenneighboring metal pillars 38 to form top dielectric layer 40, whereintop dielectric layer 40 may also be on top of, and may or may not,contact the underlying passivation layers, which may comprise siliconnitride, silicon oxynitride, silicon oxide, or multi-layers thereof.Polymer layer 40 may be formed of PBO in accordance with some exemplaryembodiments.

Next, as shown in FIG. 6, molding material 44 is molded on device die36. The respective step is shown as step 316 in the process flow shownin FIG. 23. Molding material 44 fills the gaps between neighboringthrough-vias 32 and the gaps between through-vias 32 and device die 36.Molding material 44 may include a molding compound, a molding underfill,an epoxy, or a resin. The top surface of molding material 44 is higherthan the top ends of metal pillar 38.

Further referring to FIG. 6, a planarization such as a ChemicalMechanical Polish (CMP) step or a grinding step is performed to thinmolding material 44, until through-vias 32 and metal pillars 38 areexposed. The respective step is shown as step 318 in the process flowshown in FIG. 23. Due to the grinding, the top ends of through-vias 32are substantially level (coplanar) with the top surfaces of metalpillars 38, and are substantially coplanar with the top surface ofmolding material 44.

Referring to FIG. 7, dielectric layer 46 is formed. The respective stepis shown as step 320 in the process flow shown in FIG. 23. In accordancewith some embodiments of the present disclosure, dielectric layer 46 isformed of a polymer, which may also be a photo sensitive dielectricmaterial in accordance with some embodiments of the present disclosure.For example, dielectric layer 46 may be formed of PBO, polyimide, or thelike. In alternative embodiments, dielectric layer 46 is formed ofsilicon nitride, silicon oxide, or the like. Throughout the description,dielectric layer 46 is alternatively referred to as a bottomRDL-embedding polymer layer.

Referring to FIG. 7, dielectric layer 46 is patterned in a photolithography process. The respective step is shown as step 322 in theprocess flow shown in FIG. 23. For example, in the embodiments in whichdielectric layer 46 is formed of a photo sensitive material, photolithography mask 48 is used for light exposure. Photo lithography mask48 includes transparent portions allowing light to pass through, andopaque portions for blocking light. A light exposure is then performed,wherein light (arrows) is projected to expose light-sensitive dielectriclayer 46. After the development and the baking process, openings 50 areformed, as shown in FIG. 8.

As shown in FIG. 8, through-vias 32 and metal pillars 38 are exposedthrough openings 50. In subsequent paragraphs, the portions of thestructure over release layer 22, including dies 36, through-vias 32, andthe corresponding RDLs (with some being formed in subsequent steps),etc., are in combination referred to as package 100, which includes aplurality of packages 54. In addition, scribe lines 52 are betweenpackages 52, and the edges of the bottom RDL-embedding polymer layer 46define the boundaries of packages 54. Scribe lines 52 are the regions inwhich the sawing blade will pass through in a subsequent die-sawingprocess. Accordingly, RDL-embedding polymer layer 46 does not extendinto scribe lines 52, but will be in packages 54. As a result of thepatterning, in scribe lines 52, molding material 44 is exposed.

FIG. 21 illustrates a top view of packages 54 and scribe lines 52. Asshown in FIG. 21, scribe lines 52 form a grid pattern to separatepackages 54.

Next, referring to FIG. 9, Redistribution Lines (RDLs) 58 are formed toconnect to metal pillar 38 and through-vias 32. The respective step isshown as step 324 in the process flow shown in FIG. 23. RDLs 58 may alsointerconnect metal pillar 38 and through-vias 32. RDLs 58 include metaltraces (metal lines) over dielectric layer 46 as well as vias extendinginto openings 50 (FIG. 8) to electrically connect to through-vias 32 andmetal pillar 38. In accordance with some embodiments of the presentdisclosure, RDLs 58 are formed in a plating process, wherein each ofRDLs 58 includes a seed layer (not shown) and a plated metallic materialover the seed layer. The seed layer and the plated material may beformed of the same material or different materials. RDLs 58 may comprisea metal or a metal alloy including aluminum, copper, tungsten, andalloys thereof. After the formation of RDLs 58, the openings 50 (FIG. 8)in scribe lines 52 remain not filled with RDLs 58.

Referring to FIG. 10, polymer layer 60 is formed over RDLs 58 anddielectric layer 46, for example, through spin coating. The respectivestep is shown as step 326 in the process flow shown in FIG. 23. Polymerlayer 60 may be formed using a polymer selected from the same candidatematerials as those of dielectric layer 46. For example, polymer layer 60may comprise PBO, polyimide, or the like. After the formation, polymer60 fills openings 50 (FIG. 9) that are in scribe lines 52, and coversRDLs 58.

Next, as also shown in FIG. 10, photo lithography mask 61 is placed overcomposite package 100. A light exposure is then performed, wherein light(arrows) is projected to expose polymer layer 60. After the developmentand the baking process, openings 64 (including 64A, 64B, and 64C) areformed, as shown in FIG. 11. The respective step is shown as step 328 inthe process flow shown in FIG. 23. The pad portions of RDLs 58 areexposed through openings 64C, which are discrete openings in packages54. Openings 64B are also in packages 54, and extend from the topsurface of polymer layer 60 to the top surface of dielectric/polymerlayer 46, and hence dielectric layer 46 is exposed through openings 64B.In accordance with some embodiments, as shown in FIG. 21, openings 64Bform trench rings close to scribe lines 52, for example, with thedistance between openings 64B and the respective scribe lines 52 beingsmaller than about 100 μm. Furthermore, openings 64B may be formed toencircle, and hence does not overlap, the respective dies 36 and theconductive features in the respective packages 54. Alternatively stated,dies 36 and the conductive features do not extending directly underlyingtrench rings 64B in accordance with some embodiments of the presentdisclosure, and are limited in the region encircled by trench rings 64B.

As shown in FIG. 11, the portions of polymer 60 in scribe lines 52 aremuch thicker than the portions of polymer 60 in packages 54. As aresult, in the lithography process to pattern polymer 60, residue 60′may be left after the patterning due to inadequate light exposure of thebottom portions of polymer 60 in scribe lines 52. It is also possiblethat there is no residue of polymer 60 left in scribe lines 52. It isappreciated that whether residue 60′ is left or not is affected byvarious factors including the thicknesses and the materials of layers 46and 60, the exposure conditions, and the like.

Next, referring to FIG. 12, RDLs 66 are formed to connect to RDLs 58.The respective step is shown as step 330 in the process flow shown inFIG. 23. RDLs 66 also include metal traces (metal lines) over polymerlayer 60 as well as vias extending into openings 64C (FIG. 11) toelectrically connect to RDLs 58. The material and the formation processof RDLs 66 may be similar to that of RDLs 58. Trench rings 64B andscribe lines 52 remain not filled with RDLs 66.

Referring to FIG. 13, polymer layer 68 is formed over RDLs 66, forexample, through spin coating. The respective step is shown as step 332in the process flow shown in FIG. 23. Polymer layer 68 is referred to asa top polymer layer hereinafter. Although the illustrated exemplaryembodiments show three dielectric (polymer) layers and the correspondingRDLs, the number of layers may be more or fewer than illustrated inother embodiments. Polymer layer 68 may also be formed using a polymerselected from the same candidate materials as those of dielectric layer46. For example, polymer layer 68 may comprise PBO, polyimide, or thelike. After the formation, polymer layer 68 fills openings 64A and 64B(FIG. 12), and covers RDLs 66.

Next, as also shown in FIG. 13, polymer layer 68 is patterned. Therespective step is shown as step 334 in the process flow shown in FIG.23. Photo lithography mask 70 is placed over composite package 100. Alight exposure is then performed, wherein light (arrows) is projected toexpose polymer layer 68. After the development and the baking process,openings 72 (including 72A, 72B, and 72C) are formed, as shown in FIG.14. The pad portions of RDLs 66 are exposed through openings 72C, whichare discrete openings in packages 54. Openings 72B are also in packages54, and extend from the top surface of polymer layer 68 to the topsurface of polymer layer 60, and hence polymer layer 60 is exposedthrough openings 72B. In accordance with some embodiments, openings 72Bform trench rings close to scribe lines 52 (also refer to FIG. 22).Furthermore, openings 72B may be formed to encircle, and hence does notoverlap, the respective dies 36 and the conductive features in therespective packages 54. Alternatively stated, dies 36 and the conductivefeatures in packages 54 do not extending directly underlying trenchrings 72B in accordance with some embodiments of the present disclosure,and are limited in the region encircled by trench rings 72B. In someexemplary embodiments, as shown in FIG. 14, trench ring 72B is formed onthe inner side of trench ring 64B (which is filled by polymer layer 68).

As shown in FIG. 13, the portions of polymer 68 in scribe lines 52 aremuch thicker than the portions of polymer 60 in packages 54. As aresult, after the lithography process to pattern polymer 60, as shown inFIG. 14, residue portions 68′ (FIG. 14) are left in scribe lines 52. Thethickness of residue portions 68′ may be greater than, equal to, orsmaller than the thickness of the portion of polymer layer 68 inpackages 54.

In accordance with some exemplary embodiments, trench ring 64B hasdistance D1 from the closest scribe line 52. Distance D1 may be greaterthan about 10 μm, and may be smaller than about 50 μm. The width W1 oftrench ring 64B may be greater than about 10 μm and smaller than about50 μm. Distance D2 between trench ring 64B and trench ring 72B may be inthe range between about 10 μm and about 50 μm. Width W2 of trench ring72B may also be in the range between about 10 μm and about 50 μm.

FIG. 15 illustrates the formation of Under-Bump Metallurgies (UBMs) 74and electrical connectors 76 in accordance with some exemplaryembodiments. The respective step is shown as step 336 in the processflow shown in FIG. 23. The formation of UBMs 74 may include depositionand patterning. The formation of electrical connectors 76 may includeplacing solder balls on the exposed portions of UBMs 74 and thenreflowing the solder balls. In alternative embodiments, the formation ofelectrical connectors 76 includes performing a plating step to formsolder regions over RDLs 66 and then reflowing the solder regions.Electrical connectors 76 may also include metal pillars or metal pillarsand solder caps, which may also be formed through plating.

Next, package 100 is de-bonded from carrier 20. The de-bonding may beperformed by projecting a light such as UV light or laser on releaselayer 22 to decompose release layer 22. In the de-bonding, a tape (notshown) may be adhered onto polymer layer 68 and electrical connectors76. In subsequent steps, carrier 20 and release layer 22 are removedfrom package 100. The resulting structure is shown in FIG. 16.

As shown in FIG. 16, a die saw step is performed to saw package 100 intoa plurality of packages 54, each including device die 22 andthrough-vias 32. The paths passed through by the sawing blade are markedas paths 67. The respective step is shown as step 338 in the processflow shown in FIG. 23. FIG. 22 illustrates a top view of one of packages54 sawed from package 100. It is appreciated that since the width of thesawing blade is typically smaller than the widths of scribe lines 52 asshown in FIG. 15, the resulting package 54 may include small portions ofthe original scribe lines 52.

Referring to FIG. 16 again, in the sawing of package 100, due to theresidues in scribe lines, neighboring dielectric/polymer layers 46, 60,and/or 68 may be sawed-through. Since the interface between neighboringdielectric/polymer layers 46, 60, and 68 and molding material 44 areweak parts, the upper ones of dielectric/polymer layers 46, 60, and 68may delaminate from the underlying ones of dielectric/polymer layers 46,60, and 68 and molding material 44. The delamination tends to propagatethrough the interfaces into packages 54. By forming trench rings 64B and72B, if delamination occurs, the delamination will be stopped by thetrench rings. For example, assuming delamination occurs at, andpropagates through, the interface between polymer layers 46 and 60, thedelamination will end at the position marked as 63, which are alsorings. If delamination occurs at, and propagate through, the interfacebetween polymer layers 60 and 68, the delamination will end at theposition marked as 65, which are also rings.

FIG. 16 also illustrates the bonding of package 54 with another package200. In accordance with some embodiments of the present disclosure, thebonding is performed through solder regions 98, which join the metal padportions of RDLs 26 to the metal pads in package 200. In accordance withsome embodiments of the present disclosure, package 200 includes devicedies 202, which may be memory dies such as Static Random Access Memory(SRAM) dies, Dynamic Random Access Memory (DRAM) dies, or the like. Thememory dies may also be bonded to package substrate 204 in someexemplary embodiments.

FIG. 21 illustrates a top view of package 100 and scribe lines 52. Asshown in FIG. 21, trench ring 72B forms a ring that encircles device die36, electrical connectors 76 and RDLs 58 and 66. Trench ring 64B alsoforms a ring. In accordance with some embodiments of the presentdisclosure, as shown in FIG. 21, trench ring 72B encircles trench ring64B. In alternative embodiments (not shown), trench ring 72B may beencircled by trench ring 64B. The package 54 obtained after sawingpackage 100 is illustrated in FIG. 22.

FIGS. 17 through 20 illustrate the cross-sectional views of package 100(and packages 54 therein) in accordance with alternative embodiments. Ineach of FIGS. 17 through 20, trenches 64B and 72B may form full ringsclose to the respective edges of the packages. As shown in FIG. 17,trench ring 64B and trench ring 72B overlap with each other, with thewidth W2 of trench ring 72B being smaller than width W1 of trench ring64B. Accordingly, trench ring 72B extends into the portion of polymerlayer 68 that extends into trench ring 64B.

FIG. 18 illustrates the cross-sectional views of package 100 (andpackages 54 therein) in accordance with alternative embodiments. Inthese embodiments, trench ring 64B and trench ring 72B also overlap witheach other, with the width W2 of trench ring 72B being greater thanwidth W1 of trench ring 64B. Accordingly, polymer layer 68 does notextend into trench ring 64B. Trench rings 64B and 72B in theseembodiments are merged as a large trench ring.

FIG. 19 illustrates the cross-sectional views of package 100 (andpackages 54 therein) in accordance with alternative embodiments. Inthese embodiments, there is no trench ring formed in polymer layer 60.These embodiments may be used when no residue portions of polymer layer60 are left in scribe lines 52 after the step shown in FIG. 11, andhence it is not necessary to form a trench ring in polymer layer 60.However, with more polymer layers formed, the trenches in scribe lines52 become increasingly deeper, and hence upper polymer layers such aspolymer layer 68 are more likely to have residue portions. Trench ring72B is thus formed in polymer layer 68 in these embodiments.

FIG. 20 illustrates the cross-sectional views of package 100 (andpackages 54 therein) in accordance with alternative embodiments. Inthese embodiments, trench ring 64B and trench ring 72B overlap with eachother, with the width W2′ of trench ring 72B being smaller than width W1of trench ring 64B. Accordingly, trench ring 72B extends into theportion of polymer layer 68 that extends into trench ring 64B. Inaddition, trench rings 72B of two packages on the opposite sides ofscribe line 52 extend into scribe line 52 and are merged together. As aresult, in the final structure after package 100 is sawed apart, trenchring 72B extends to the edges of packages 54.

The embodiments of the present disclosure have some advantageousfeatures. Trench rings are formed in the polymer layers of InFOpackages. The trench rings may be used as delamination stoppers in thesawing of packages to prevent the delaimination between polymer layersto propagate into the inner portions of packages. An advantageousfeature of the embodiments of the present disclosure is that theformation of trench rings is achieved simultaneously as the formation ofopenings for UBMs and RDLs, and hence no additional manufacturing costis involved.

In accordance with some embodiments of the present disclosure, a packageincludes a device die, a molding material encircling the device die,wherein a top surface of the molding material is substantially levelwith a top surface of the device die, and a bottom dielectric layer overthe device die and the molding material. A plurality of RDLs extendsinto the bottom dielectric layer and electrically coupling to the devicedie. A top polymer layer is over the bottom dielectric layer, with atrench ring penetrating through the top polymer layer. The trench ringis adjacent to edges of the package. The package further includes UBMsextending into the top polymer layer.

In accordance with alternative embodiments of the present disclosure, apackage includes a device die, and a molding material encircling thedevice die, wherein a top surface of the molding material issubstantially level with a top surface of the device die. A through-viapenetrates through the molding material, wherein a top surface of thethrough-via is substantially coplanar with the top surface of the devicedie. The package further includes a first polymer layer over and incontact with the device die, the through via, and the molding material.A plurality of RDLs extends into the first polymer layer to electricallycouple to the device die and the through-via. A second polymer layer isover the first polymer layer and the plurality of RDLs, wherein a firsttrench ring extends from a top surface of the second polymer layer to atop surface of the first polymer layer. The package further includes athird polymer layer over and in contact with the second polymer layer,wherein a second trench ring extends from a top surface of the thirdpolymer layer to a top surface of the second polymer layer. UBMs extendinto the third polymer layer.

In accordance with yet alternative embodiments of the presentdisclosure, a method includes molding a plurality of device dies in amolding material, and planarizing the plurality of device dies and themolding material, wherein top surfaces of the device dies are level witha top surface of the molding material. The method further includesforming a first polymer layer over and contacting the plurality ofdevice dies and the molding material, and patterning the first polymerlayer to form a first plurality of openings, with metal pillars of thedevice dies exposed through the first plurality of openings. Scribelines are formed by the step of patterning the first polymer layer. Themethod further includes forming a plurality of redistribution lineshaving via portions penetrating through the first polymer layer, forminga second polymer layer over the first polymer layer, and patterning thesecond polymer layer to form a second plurality of openings and a firstplurality of trench rings, with each of the first plurality of trenchrings encircling one of the plurality of device dies. The firstplurality of trench rings is separated from each other by the scribelines. A plurality of UBMs is formed to extend into the second polymerlayer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: encapsulating a first devicedie and a second device die in an encapsulating material; forming afirst dielectric layer over and contacting the first device die, thesecond device die, and the encapsulating material; performing a lightexposure on the first dielectric layer using a lithography mask;developing the first dielectric layer that is light-exposed tosimultaneously forming a first opening overlapping the first device die,a second opening overlapping the second device die, and a trenchoverlying a scribe line portion of the encapsulating material betweenthe first device die and the second device die; and sawing theencapsulating material, wherein a kerf of the sawing passes through thetrench.
 2. The method of claim 1, wherein after the sawing, the firstopening and the second opening are separated into a first package and asecond package, respectively.
 3. The method of claim 2, wherein thetrench is separated by the sawing into a first portion in the firstpackage and a second portion in the second package.
 4. The method ofclaim 1 further comprising: forming a second dielectric layer comprisinga first portion over and contacting the first dielectric layer, and asecond portion in the trench; patterning the second dielectric layer toform an additional trench in the second dielectric layer; and forming athird dielectric layer over and contacting the second dielectric layer,wherein the third dielectric layer extends into the additional trench.5. The method of claim 4, wherein the additional trench forms a trenchring encircling a region directly over the first device die.
 6. Themethod of claim 4 further comprising patterning the third dielectriclayer, wherein in the patterning the third dielectric layer, a portionof the third dielectric layer extending into the additional trench isremoved.
 7. The method of claim 1, wherein after the first dielectriclayer is developed, a portion of the first dielectric layer remainsunder the trench.
 8. A method comprising: encapsulating a device die inan encapsulating material; forming a first dielectric layer over andcontacting the device die and the encapsulating material; simultaneouslyforming first openings and a trench in the first dielectric layer,wherein conductive features of the device die are exposed through thefirst openings; forming first Redistribution Lines (RDLs) to fill thefirst openings; and forming a second dielectric layer over the firstRDLs, wherein the second dielectric layer fully fills the trench.
 9. Themethod of claim 8 further comprising: patterning the second dielectriclayer to form: a first trench ring penetrating through the seconddielectric layer; and second openings encircled by the first trenchring, wherein a top surface of the first dielectric layer is exposed tothe first trench ring, and top surfaces of the RDLs are exposed to thesecond openings.
 10. The method of claim 9 further comprising: formingsecond RDLs to fill the second openings; and forming a third dielectriclayer having a first portion over the second RDLs and a second portionextending into the first trench ring; and patterning the thirddielectric layer to form a second trench ring.
 11. The method of claim10, wherein in a top view of the device die, a first one of the firsttrench ring and the second trench ring encircles a second one of thefirst trench ring and the second trench ring.
 12. The method of claim10, wherein the second trench ring overlaps the first trench ring, and atop surface of the first dielectric layer is exposed to the secondtrench ring.
 13. The method of claim 10, wherein the second trench ringoverlaps the first trench ring, and after the second dielectric layer ispatterned, a portion of the second dielectric layer remains in the firsttrench ring.
 14. The method of claim 9 further comprising sawing throughthe first dielectric layer, the second dielectric layer, and theencapsulating material to form a package, wherein a kerf of the sawingpasses through the trench.
 15. A method comprising: encapsulating afirst device die in an encapsulating material; forming a firstdielectric layer over and contacting the first device die and theencapsulating material; simultaneously forming openings and a trench inthe first dielectric layer, wherein conductive features of the firstdevice die are exposed through the openings, and the encapsulatingmaterial is exposed through the trench; and forming Redistribution Lines(RDLs) to fill the openings, wherein after the RDLs are formed, theencapsulating material is exposed through the trench.
 16. The method ofclaim 15, wherein the encapsulating material further encapsulates asecond device die therein, and the trench overlaps a scribe line betweenthe first device die and the second device die.
 17. The method of claim15 further comprising: forming a second dielectric layer having a firstportion over and contacting the first dielectric layer, and a secondportion extending into the trench; and patterning the second dielectriclayer to at least partially remove the second portion of the seconddielectric layer.
 18. The method of claim 17, wherein after the seconddielectric layer is patterned, the encapsulating material is exposedthrough the trench.
 19. The method of claim 17, wherein after the seconddielectric layer is patterned, the second portion of the seconddielectric layer has a remaining portion in the trench.
 20. The methodof claim 15 further comprising sawing through the trench.